1. Field of the Invention
The present invention relates to a method for checking the power status, of batteries, in particular to a method that can considerably enhance the estimation of the remaining power of the tested battery.
2. Description of Related Arts
The power for emergency power systems or uninterrupted power supply (UPS) systems generally comes from batteries. When the normal power supply is interrupted, the power source can be automatically switched to an emergency system that is capable of supplying the necessary power during the power outage. It is therefore very important to keep the emergency systems and the storage batteries in top operating conditions at all times. A number of techniques for checking the power status of these batteries have been discussed by prior art patents. One proposed a monitoring device for simultaneously monitoring of the battery characteristic data on several batteries on a continuous basis. These characteristic data include the discharging current, operating temperature, terminal voltage and remaining power capacity. These characteristic data can be accurately measured with an appropriate means except the remaining power capacity. Though important for a battery, the true power status of a battery at any given moment is hard to come by with acceptable confidence. FIG. 4 shows the relationship between the battery capacity and the amount of current output of a typical battery. Using a lead acid cell as an example, high current output of the battery generally results in small battery capacity in ampere/hour. In further analysis of the correlation between the two variables, it is found that the amount of discharging current of the battery is dependent on the electrolysis process of the electrode material with the electrolyte on the inner electrode plates of the battery. When the battery is in a high discharge rate with a large discharging current, H2SO4 material will tend to accumulate in the gap between the electrode plates where the chemical reaction is taking place, causing the compound material to be changed to PbSO4, thus blocking the infiltration of the compound material to the inner electrode plates, where no chemical reaction takes place. The battery capacity therefore is decreased drastically at the high discharge rate. On the contrary, when the battery is set to a low discharge rate with a small discharging current, H2SO4 is able to infiltrate to the inner electrode plates by capillary action to allow a complete chemical reaction on all electrode plates, thus the battery capacity is effectively increased. From the above experiment, it is known that the remaining power capacity of a battery tends to be inversely related to the amount of discharging current from a discharging battery.
However, even with the inverse relationship between the remaining power capacity and the discharging current, it is still difficult to come up with an acceptable method of checking the power status for any type of battery. The main problem is that different types of batteries exhibit different characteristics. There are so many types of batteries available, it is impossible to apply the above formula universally to estimate the remaining power capacity.
For a lead acid cell, as an example, the typical potential for chemical reaction is 2V, but the termination voltage will vary in accordance with the amount of current output and the type of battery used, which can be anywhere from 1.671V 1.7V, 1.750V, 1.83V, to 1.9V. The following two cases fully demonstrate that different battery capacity will be produced for different amounts of current output and termination voltage.
Case 1: when the termination voltage is known to be 1.750V, a 2V 1000A/h battery with a discharge rate of 100 A will be able to last for ten hours until the voltage eventually drops to 1.750V.
Case 2: when the termination voltage is known to be 1.832V, a 2V 1000A/h battery with a discharge rate of 250 A will only last for four hours until the voltage eventually drops to 1.832V.
In both cases, even for two batteries with the same specifications and 100% battery capacity, the performance of the batteries will not be the same considering the variables such as the discharging current, battery makes, manufacturing process, and inherent quality, which will all be related to the termination voltage of a battery thus affecting their battery capacity. Also, operating temperature is another factor that may affect the battery capacity. The foregoing experiments only prove that it is grossly inadequate to make any estimation of the remaining power capacity in a battery using a universal formula. Another prior art patent attempted to use the terminal voltage and the amount of discharging current to calculate the discharge rate, which is then multiplied by the amount of discharging current to generate the remaining power capacity of a battery, but does not consider the above mentioned factors that potentially will affect the battery capacity. It is apparent that this is a troublesome aspect for the maintenance of the storage batteries as they have to be kept in top condition at all times to meet the emergency needs.